vic-ii pal colors

Hi. I noticed that if you capture analog C64 video with the comb filter turned 
off there is quite a difference in color saturation and/or hue between even and 
odd lines.

I thought that the colors were generated by adding a weighted sum of sine and 
cosine signals, but inverting one of the inputs (which is done in odd lines in 
PAL systems) should not have any effect of the overall amplitute, unless I am 
very much mistaken.

Has any more research been done into this?

Cheers
Michiel

FWIW I have taken some measurements here:
http://www.michiel.boland.org/c64_colors.html